The Linux Administration group is for the discussion of technical issues technical issues that arise during the administration of Linux systems, including maintaining the operating system and supporting end-user applications.

It means that you have configured your postfix mta to run as the user
postfix nad you are currently logged into your system as root user. And you
have configured your current server where you are logged in to as a master
postfix server. Thats why it is showing as master and smtpd both listening
on port 25, but don't worry as it is not a issue your server will work fine.

It looks fine. but if the problem persists then you can check the following.

Have you added the mail server ip firsr three octets in /etc/mail/access
file.
if it is done you can check in postfix configuration file whether you have
added any ip or domain in reject list
alternatively you can check your smtpd configuration to check whether there
is any abnormality there.

I am not seeing any problem from this output. but it will be worth to check
your relaying configuration in /etc/mail/access and you can also check your
mrp protocol configuration files such as dovecot.conf for imaps or pops for
any incoming mail issues there.

How have you configured mail storage? Because remember when the Server recives it needs to distribute the email to various local inboxes and if this is poorly done you cannot receive. I normally use MAILDIR as I find it easy to manage my users, however in a situation where you are handling throusands of email addresses MAILDIR is not an ideal solution. Read more on MailDir here http://en.wikipedia.org/wiki/Maildir and also this article is very useful http://www.linuxmail.info/mbox-maildir-mail-storage-formats/

This takes me to a new question I may have missed some information, POSTFIX is not a mailserver but rather a MTA ( Mail Transfer Agent) What mail server are you using ? This can help me to underdtand the configuration we are talking about. I normally use DOVECOT Mail Server configured to run Maildir for mail storage and a POSTFIX MTA transafering mails to Maildir for individual accounts.